Telephone exchange system



E. v'RooM ET L,

TELEPHONE EXCHANGE SYSTEM Filed Aug. 17, 1926 7 Sheets-Sheet l Z W I Z d. .W/ d M Aug. 20, 1929.. E. yRooM ET AL 1,725,323

TELEPHONE EXCHANGE SYSTEM Filed Aug. 1'7, 1926 '7 Sheets-Sheet 2 I mi U i AV/mm kite/7; r rdm mzzmz Aug. 20, 1929. E. VROOM ET AL TELEPHONE EXCHANGE SYSTEM Filed Aug. 17, 1926 TSheets-Sheet 3 Aug. 20, 1929. E. VROOM ET AL 1,725,323

TELEIEHONE EXCHANGE SYSTEM Filed Aug 17, 1926 7 Sheets-Sheet 4 Meryl/ml fepeafer 6 Aug 20, 1929. E. VROOM ET AL 1,725,323

TELEPHONE EXCHANGE l'SYSTEM Filed Aug. 17, 1926 7 Sheets-Sheet 5 Aug. 20; 1929. E. VROOM ET AL TELEPHONE EXCHANGE SYSTEM Filed Aug. 17, 1926 '7 Sheets-Sheet 6 Aug. 20, 1929..

E. VROOM ET AL TELEPHONE EXCHANGE SYSTEM Filed Aug. 17, 1926 7 Sheets-Sheet 7 O O O Pepeafer fiepeafer [in 4rd W000? Patented sa 2e, teas.

EDWARD VROOM, 0F QS'SEIJING, AND FERDINAND S. ENTZ, OF MOUNT VERNON, NEW YORK, ASSIGNOBS TO BELL TELEPHQNE LABORATORIES, INCOBPQRATED, 0F NEVI YORK, N. Y., A CORPORATION OF NEW' YORK.

TELEFHQNE-EXCKANGE SYSTEM.

This invention relates to telephone switching systems and more particularly to the automatic selection of speech amplifying and repeating apparatus and the insertion of the same in toll connections.

Systems, such as those disclosed in Patent No. 1,647,796, issued to L. L. Glezen, S. P. Shackleton and E. Vroom Nov. 1, 1927, and the application of E. Vroom and J. A.

Krecek, Serial No. 39,882, filed June 27, 1925,.have been devised for automatically inserting repeating amplifiers in toll connections. In these cases toll cord circuits are arranged for toll lines that do not require the addition of repeaters and toll lines that do require such an addition. The arrangement is such that an automatic discrimination is made between the two kinds of toll lines when a cord circuit is employed to interconnect a pair of lines. When arepeater is required, this discriminating arrangement functions to start the automatic selection and connection of the repeater between the two toll lines. A selecting mechanism is associated with each of a plurality of cord circuits. Each of said selectors is arranged to be automatically started by the discriminating means to hunt f and con nect the associated cord circuit with an idle repeater, a plurality of which are provided for the common use of said cord circuits. Each repeater is provided with two line finder switches so arranged that as soon as the repeater is engaged by a cord circuit one of the associated line finders begins to hunt for one of the toll lines associated with the cord circuit and when this toll line is found, the other associated line finder be gins to hunt for another toll line connected to the cord circuit.

According to the present invention toll lines are arranged in groups, each group being provided with a group of links comprising finder switches which respond to the interconnection or any two lines in such a manner that two of said links operate simul taneously, one to make connection to one side and the other link to make connection with the opposite side of a repeater ampliher. In this way the epeater is automatically inserted in the toll connection.

Each link includes a line finder and a repeater finder. One half of the links of each group are connected to the incoming Application filed August 17, 1926. Serial No. 129,682.

ends of a common group of repeaters, the outgoing ends of which are connected to the terminal banks of the remaining ha i the repeater finders of each group. The terminal banks of said repeater finders in a group are multipled to the terminal banks of the corresponding repeater finders in other groups of lines. Any one of the repeaters vin this common group is thereby accessible for insertion between any two of said lines in these various groups. A connection between two lines may therefore extend from one line through the switches of one link to a repeater and out from said repeater through the switches of another link to the other line. The advantage of arranging the lines in groups and interposing links the above description between the lines and a common group of repeaters in the above nanner is that a small number 01 repeaters may be provided to serve a comparatively large number of lines. t is also noted that within certain limits the larger the number of lines in the individual group the relatively less number of repeaters is required to take care of the probable simultaneous number of connections requiring repeaters inserted between lines.

The cords for use in interconnecting lines may also be arranged in groups at different operators positions and each cord may be provided with a repeater selector switch whereby an idle repeater in the common group may be selected. It is of advantage to limit the number of repeaters to which each repeater selector may have access to a num ber less than the total number of repeaters available for the total number of groups of cords and it is not necessary to make the same repeaters available to the same repeater selectors in the same group. It may in fact be of advantage to stagger the repeaters connected to the repeater selectors in accordance with some predetermined scheme to distribute the use of the repeaters in a uniform manner as is well known in the art.

This invention has been illustrated in the accompanying drawings in which Fig. 1 illustrates the incoming end of one toll line requiring the addition of a repeater. Fig. 2 illustrates one of the links associated with the line shown in Fig. 1. In this case a link that is employed for connecting this line with input ends of repeaters is shown.

Figs. 3 and 4 illustrate a cord circuit and its associated repeater selector and a repeater, the repeater merely indicated by means of an inclosure. These figures also show various common circuit and switching arrangements for preventing more than one intel-connection of toll lines from taking place at any one time.

Figs. 5 and 6 illustrate the incoming end of another toll line requiring the addition of a repeater and one of the associated links. In this case the link employed for connecting this line to output ends of repeaters is shown.

Fig. 7 is a diagrammatic representation of a typical grouping of toll lines, links, repeaters, repeater selectors, and cord circuits in accordance with this invention.

Fig. 8 illustrates how the Figures 1 to 6 may be arranged for the purpose of reading the circuits thereof.

Referring now to Fig. 7, the grouping in accordance with this invention of the various equipments may be carried out as follows: For example, toll lines may be divided into two groups, 1 and 2, with 100 lines in each group. The lines of each group may be associated with approximately 50 links, 25 of which are employed for extending connections from the lines in this group to the incoming ends of repeaters and the other 25 of which maybe employed for extending connections to the lines in this group from the outgoing ends of repeaters. It will be noted that the left hand switches or line finders of thelink groups 5 and 6 have their terminals connected to lines in group 1 and that the connection from each line is multipled to a terminal of each of these line finders. On the other hand, the right hand switches or repeater finders of the links in group 5 have their terminals multipled and connected to the incoming ends of a group of repeaters represented at 10 and 12, While the repeater finders in group 6 have their terminals similarly multipled and connected to outgoing ends of the repeaters 10 and 12. Similarly the lines in group 2 are connected to two groups of links 15 and 16. The terminals of the line finders and repeater finders in these groups are connected in the same man nor as the terminals of the line finders and repeater finders in groups 5 and (3 respectively. In an arrangement of this kind approxi mately 415 repeater units may be provided for the 200 lines and the incoming and outgoing ends of these repeaters may be connected The arrangement of the repeater selector-s and cord circuits and their relation to the repeaters may for example be as follows: There may be from 10 to 20 operators positions each equipped with 9 cords. Two of these positions 20 and 21 have been illustrated with tWo cord circuits each. Each of the cord circuits is associated with a repeater selector such as 25, 26, 27, 28 and the terininals of these selectors are multipled together in any convenient staggered arrangement, so that all of the repeaters may be employed for approximately the same number of times. The capacity of the repeater selectors may therefore be less than the total number of repeaters available, for example, from 20 to 25 repeaters may be connected to each repeater selector.

Referring now to Figs. 1 to 6 the general scheme of interconnecting toll lines and inserting repeaters into these connections in accordance with this invention may be outlined as follows:

Let is be assumed that the toll line A is tobe connected through a repeater with. a toll line B and that cord circuit C is to be used for the establishing of this connection. A call incoming over line A is observed by the inward operator on the usual toll board by the lighted lamp 100. After inserting the answering plug of an ordinary toll cord into jack 101 of line A and communicating with the operator at the distant end of line A, it is found that the call requires a through connection. This inward operator will switch the call to a through operators position causing lamp 102 to light. The through operator has access to a plurality of cords such as C and observing the lamp 102 of line A lighted this operator inserts plug 300 of cord G into jack 103, of line A and operates the talking key 301 to connect her telephone set to line A for the purpose of communicating with the operator at a distant end to ascertain the destination of the desired. connection. After having received the desired information, the through operator noW inserts plug 303 into jack 500 of line B and restores the talking key 301.

As it has been assumed that both line A and B require the insertion of a repeater, these lines have special electrical characteristics on their sleeve circuits that will initiate, When the toll lines are connected to the cord circuit, the automatic operation of inserting a repeater into the connection. For this purpose there is provided a so-called lock-out selector switch or cord. finder, one of which is indicated at D. Each cord finder is common to a position or group of cords. The cord finder D Will noW start to find the cord 3 and when it is found, the cord finder remains associated with the cord until the operations for inserting a repeater in the connection are completed. This is in order to prevent any other cord circuit in this group from being selected until cord 0 releases'the finder. As soon as the cord finder D finds the cord circuit C, it starts op erations to associate a secondary lock-out circuit or position finder indicated at E. This finder is common to all the groups of cords in the system. Position finder E remains associated with the cord circuit C until the complete sequence of operations for inserting a repeater into the connection has been etfected and functions to prevent any other cord circuit in this or any other group from starting the selection of a repeater until cord circuit C has completed its functions in this respect. The association of the position finder takes place immediately provided no other cord in the system is going through the process of inserting a repeater in a connection. The reason for the provision of a cord finder for each group of cords and a common position finder for all the groups of cords inthe system is to insure that only one connection of a repeater between toll lines may take place at any one time. However, in order not to delay the automatic connection of repeaters any longer than is absolutely necessary, the cord finders of the various groups of cords may operate to find cords interconnecting toll lines independently and simultaneously and prepare the associated circuits to the point where the common position finder begins to operate to permit one cord circuit at a time to complete the repeater selecting and connecting functions. This arrangement of cord finders and position finders may be applied in different ways in different systems. For example, if the number of groups of cords is very large divisions may be made requiring additional position finder circuits to prevent'too many groups of cords from depending on a common finder circuit.

Once the cord circuit C has assumed control over the position finder E it starts its repeater selector, indicated at F to hunt for an idle repeater. One of these repeaters has been indicated at G, merely by means of an inclosure with all the leads from the links and the repeater selector F shown leading into the same. As the repeater itself forms no part of this invention and as any repeater of any well known arrangement may be used, it is thought that this representation will be sufficient. The repeater selectors and the cord finder selectors may be of any well known type having a series of terminal banks with brushes arranged to travel thereover in steps under the control of stepping magnet mechanisms.

When the repeater selector F finds an idle repeater, certain electrical conditions are established for the sleeve circuits of the lines A and B to cause an idle link of the group associated with line A to be seized for connecting this line to the incoming end of the repeater G and an idle link of the group associated with line B to be seized for connecting this line to the outgoing end of repeater G. It will be recalled from the previous description that each group of lines has access to a plurality of links which'are divided in pairs, one of each pair being arranged for connecting lines to incoming ends 01": the repeaters and the other for connecting lines to outgoing ends of repeaters.

In Fig. 2 has been shown in detail a link circuit H of a group of links for connecting lines in the group of which line A is' one to the incoming end of a repeater, while the companion link for connecting anyone of this group of lines to the outgoing end of a repeater has been shown merely by an inclosure marked 1. Similarly in Fig. 6 has been shown in detail a link K of a group of links for connecting anyone of the group of lines of which B is one to the outgoing end of a repeater while the companion link for connecting anyone of this group of lines to the incoming end of a repeater has been indicated by an inclosur'e marked L. The construct-ion of the line finder switches of these links may be of the usual well known Strowger type having the terminal banks arranged in horizontal layers with a brush traveling in a vertical followed by a horizon tal step-by-step movement and having a vertical row of terminals for hunting for the level or layer in which to hunt for the wanted connection. As switches of this type are well known in the art no further detailed description has been made of their construction. Each link comprises two line finders, for example, the link H consists of a line finder M for finding a line such as A and a line finder N for finding the incoming end of a repater while the link K consists of a line finder O for finding a line such as B and a line finder P for finding the outgoing end of a repeater. In general the connection of the repeaters with the lines A and B is accomplished by having the line A seize, for example, the idle link H and start finders M and N to hunt respectively and simultaneously for line A and repeater G, and by having the line B seize, for example, the idle link K and start finders O and P to hunt respectively and simultaneously for line B and repeater G. It should be pointed out at this time that the operations of links H and K also take place simultaneously so that no time is lost in finding the lines and the repeater and connecting them together.

As soon as the links have associated the lines with a. repeater, the cord and position finders are released so that the cord finder becomes available for other cords in the group to which cord C belongs and so that the position finder becomes available for any other cord of this or another position. Circuit changes will now take place to separate the two lines from the cord C and connect them to the repeater G through the links and at the same time connect the proper networks, N and N in this case to balance the lines and also remove certain short-circuits in the repeater to make it operative.

Transmission may then take place through the repeater while the connection through the cord circuit is opened. However, the usual ringing bridge is left across the toll line conductors so that supervisory signals may be received in the cord circuit over the sleeve circuits. Arrangements are also made whereby whenever the talking key of the cord circuit is operated, the repeater is cut out from the connection which now will extend through the cord circuit; Monitoring keys are also provided whereby connections from the repeater to the operators telephone set may be established through the repeater selector.

When either one of the plugs of the cord C is withdrawn from a line jack, the repeater is released from the connection. The repeater selector brushes and the cord finder brushes remain in the position in which they were last used, while the line finders of the links are returned to normal positions. The sleeve circuit of the line still connected to the cord remains in a busy condition.

F or the purpose of providing against failure of any partof the system during the establishing of a connection involving a re peater, a time delay circuit indicated by T1 is used. Each connection is allowed a certain time, for example, five seconds in which to be completed. If completed within this time, the time circuit is restored to normal but if not completed within this allotted time, the time circuit functions to give an alarm indicating which cord circuit is involved and also cause the release of the cord finder and position finder involved to allow the completion of connections through other cords to take place. The arrangement is also such that the toll operator receives a signal when all of the repeaters are busy.

Cord circuits such as C are also arranged for interconnecting ordinary toll lines that do not require the addition of repeaters. As this invention is essentially concerned with the inclusion of repeaters in toll line c011- nections, the following detailed description will be confined to a description of the functions taking place under such conditions.

As stated, when a call comes in over line A it is observed by the inward operator at the usual toll board by the fact that the lamp 100 is lighted. This lamp is lighted by the signal incoming over line A to operate relay 105 which in turn causes the release of relay 106 over an obvious circuit and the release of relay 106 closes a circuit for the operation of relay 107 as follows: battery, left hand winding of relay 107, outer left hand armature and back contact of relay 108, armature and back contact of relay 106 to ground. Relay 107 in operating closes a locking circuit for itself through its right hand winding, armature and front contact to battery at the makebefore-break contacts of relay 108. A circuit is also closed from this battery for the lighting of lamp 100 over a circuit as follows: battery, make-before-break contacts of relay 108, right hand armature and front contact of relay 107, make-before-hreak contacts of relay 110, inner right hand armature and back contact of relay 111, lamp 100 to ground. The inward operator answers this call by inserting the answering plug of an ordinary cord into jack 101 and connects her telephone set through this cord to the line A. If it is found that the call requires a through connection this inward operator transfers the call to a through operators position.

It should be noted that the toll cord C shown in Fig. 3 may also be used by the inward operator for this purpose. The transfer of the call to the through position, if a cord like C is used, may be accomplished by the operation of the key 305 which causes battery to be applied to the ring spring of jack 101 for effecting the transfer. A circuit will now be completed from battery through relay 306 and a resistance 307 in parallel, through resistance 308, key 305, the splitting key 310, the lower make-beforebreak contacts of relay 311, which is operated as described hereinafter, ring terminals of plug 300 and jack 101, retardation coil 113, left winding of relays 111 and 110 in series to ground. The character of resist ance 308, of the relay 306 and of resistance 307 are such as to cause only the operation of relay 111 as'relay 110 is marginal. The operation of relay 111 opens the circuit for lamp 100 and transfers this circuit at the inner right hand armature and front contact of relay 111 to lamp 102, which lights at the through operators position. A locking circuit is provided for relay 111 through this right hand armature and front contact. It should be understood that the talking key of the cord circuit used by this inward operator when operated causes the operation of relay 311 for the closing of this circuit through the ring conductor of the cord. The operation of the cord 0 to cause this effect will be described later. v

Lamp 102 in lighting at the'through operators position indicates that a through connection is desired. The through operator now inserts the plug 300 of cord G into jack 103 and the inward operator removes the plug corresponding to plug 300 from jack 101. The through operator then actuates talking key 301 to connect her telephone set to line A for the purpose of communicating with the operator at the distant end of toll line A o ascertain the destination of the desired connection. The first effect, after the insertion of plug 300 into jack 103 and before the key 301 is operated, will be the lighting of lamp 313, and the operation of relays 314 and 118 over a circuit as follows: battery, lamp 313, and battery, winding of relay 314 to the inner upper normal contacts of key 301, left hand armature and back contactof relay 316, sleeve terminals of plug 300 and jack 103, left hand armature and back contact of relay 116, make-before-break contacts of relay 117, winding of relay 118 to ground. The electrical condition of this circuit is such that relay 119 although marginal is also operated over a continuation of this circuit to a ground at the makebefore-break contacts of relay 120. The lighting of lamp 313 indicates to the through operator that the talking key 301 has not yet been operated. The operation of relay 118 closes a circuit for the operation of relay 108 as follows: battery, left hand winding of relay 108, armature and front contact of relay 118 to ground. The operation of relay 108 causes the release of relay 107 so that the lamp 102 is extinguished.

If the through operator now operates talking key 301 to associate her telephone set with the cord C, relay 311 is operated over a circuit as follows: battery, lower winding of relay 311, lower outer made contacts of key 301, make-before-break contacts of relay 319 to ground. The operation of key 301 also closes a circuit for the operation of relay 321 as follows: battery, upper winding of relay 321, to the ground at the makebefore-break contacts of relay 319. \Vith the operation of relay 311 an obvious circuit is closed for the operation of relay 319 which in turn transfers the ground from its make-before-break contacts to its armature for lamp 313 and relay 314 from'the sleeve circuit through the upper middle made contacts of key 301 to the operators position circuit, indicated by the letter Z, where it encounters ground through a resistance 320. The sleeve circuit itself is transferred through to the relays 322 and 323 of the operators position circuit Z. Lamp 313 is now extinguished as the resistance 320 is too high to permit it to remain lighted, but

not sufficiently high to release relay 3141. The extinguishing of lamp 313 indicates that the talking key has been operated. Relay 322 is now operated but marginal relay 323 remains in unoperated condition due to the high resistance of the winding of relay 119 which also releases due to its marginal character and the fact that the resistance of the windings of relays 322 and 323 are higher than the resistance of lamp 313 in parallel with the winding of relay 314. The circuit for these relays is as follows: battery, winding of relay 322, winding of re lay 323, right hand armature and back contact of relay 325, upper inner armature and front contact of relay 321, upper inner made contacts of key 301, left hand armature and back contact of relay 316, sleeve terminals of plug 300 and jack 103, left hand armature and back contact of relay 116, makebefore-break contacts of relay 117, winding of relay 118 to ground and winding of relay 119 to ground. The operation of relay 322 closes an obvious circuit for relay 329 and also an obvious circuit for the operation of relay 331. The operation of these relays, however, has no effect at present on the circuits. The release of the marginal relay 119 closes a circuit for the operation of relay 120 as follows: battery, winding of relay 120, armature and back contact of relay 119, armature and front contact of relay 118 to ground. The operation of relay 120 opens the circuit through its make-before-break contact to ground for relay 119, so that this relay can not again become operated as long as relay 118 remains operated, and also closes a circuit for the operation of relay 122 as follows: battery, winding of relay 122, right hand armature and back contact of relay 123, left hand armature and front contact of relay 120 to ground. The operation of relay 122 closes an obvious circuit for the operation of relay 117. Relay 118 is maintained operated to the sleeve circuit through the resistance 125 while the connection of the sleeve through the left hand armature and front contact of relay 117 to battery causes the release of relay 322. The release of relay 322 causes the operation of relay 325 as relay 329 is slow to release so that a momentary ground for the operation of relay 325 is provided from the armature and back contact of relay 322 through the armature and front contact of relay 329. The operation of relay 325 opens the sleeve circuit for relays 323 and 322 at the right hand armature and back contact of this relay and closes a circuit for the operation of relay 330 as follows: from battery, left hand armature, and front contact of relay 117, left hand armature and back contact of relay 116, sleeve terminals of jack 103 and plug 300, left hand armature and back contact of relay 316, inner upper made contacts of key 301, upper winding of relay 330, middle lower armature and front contact of relay 321, outer left hand armature and front contact of relay 325 to ground. Relay 330 in operating closes an obvious locking circuit for itself under the control of relay 314 which, it will be remembered, is maintained operated through a resistance 320 to ground. The operation of relay 117 closes an obvious circuit for the operation of relay 123 which new locks up through its right hand armature and front contact to ground at the left hand armature and front contact of relay 120 and this relay 123 in operating opens the circuit for relay 122 which opens that of relay 117. Re lay 117 in releasing removes the battery from its left hand front contact and as relay 325 was only momentarily operated, due to the release of relay 329, a circuit is now again completed for the reoperation of relay 322 and the maintaining of relay 118 operated. The reoperation of relay 322 again closes the circuit for relay 331 which is now held operated. The above mentioned cycle of operations therefore leaves the circuits in such a condition that in Fig. 3 relays 322, 325, 330, 331, 311, 314 and 321 are operated and lamp 313 is extinguished, while in Fig. 1, relays 118, 120, 123, and 103 are operated while lamps 100 and 102 are extinguished.

The operators telephone set is now connected through talking key 301 from the tip conductor of toll line A through the tip terminals of jack 103 and plug 300, upper make-before-break contacts of relay 311, lower right outer normal contacts and up per inner left normal contacts of ringing key 335, right hand upper normal contacts of splitting'key 310, armature and front contact of relay 331 to one side of the operators telephone set and from the ring conductor of toll line A to the ring terminals of ack 103 and plug 300, lower make beforebreak contacts of relay 311, inner lower normal contacts of ringing key 335, lower right normal contacts of splitting key 310 through normal contacts of key 305 to the other side of the operators telephone set.

After the through operator has received the desired information from the operator at the distant end of toll line A she will coming endof toll line A with the cord circuit C, to cause the operation of various relays and lamps. For example, the relays thatwill be maintained operated in toll line Bare 518, 520, 523 and 508 while in the cord circuit C, lamp 337 is extinguished and relays 341, 372, 344, 339 and 338 are maintained operated. The fact that relay 344 is operated connects through the operators telephone set to the toll line B so that the operator will now be able to talk to the operator at the distant end of toll line B to give this operator the information necessary for the completion of the connection to the wanted subscribers line; The talking connection in this case may be traced from the tip conductor of toll line B through the tip terminals of jack 500 plug 303, upper outer armature and front contact of relay 311, upper inner right normal contacts of ringin key 335, left hand upper normal contacts of splitting key 310, armature and front contact of relay 344 to one side of the operators telephone set, while the other side of the operators set is connected from the ring conductor of toll line B, ring terminals of jack 500, and plug 303, inner outer lower armature and front contact of relay 311, lower right normal contacts of splitting key 310, through the contacts of key 305 to the opposite side of the operators telephone set.

It should be noted that the operator at the distant end of the toll line B may be rung by operating the ringing key 335 to the leftto apply battery through relay 306 and resistance 307 to the upper outer right made contacts of ringing key 335 through the upper outer armature and front contact of relay 311, tip terminals of plug 303, and

jack 500, retardation coil 526, ringing relay 527 to ground. The operation of this relay applies ringing current from the usual source to the tip and ring terminals of toll line B. On the completion of instructions to the distant operator key 301 may be restored.

On the connection of the two lines A and B to the cord circuit C relays 330 and 330 are operated. These relays complete a circuit from ground to the position finder E, provided the piston finder is not in use with another cord. This ground will operate the stepping magnet 400 of cord finder D to start this finder to hunt for cord C. Battery for operating stepping magnet 400 is supplied to the terminals of bank 401 from the idle or busy cord circuits associated therewith over the upper outer armature and back contacts of relays corresponding to relays and 330. The only cord that has no battery on its terminal in bank 401 is the cord 0. A circuit will therefore be com: pleted from a battery through the brush of bank 401, winding of stepping magnet 400 and its armature and back contact, left hand armature and back contact of relay 403, common lead 342, left hand armature and back contact of relay 340, upper inner armature and front contact of relay 339, outer right hand armature and back contact of relay 345, upper inner armature and front contact of relay 330 to ground. The stepmanne: to be hereinafter described.

ping magnet 400 will therefore continue to operate until the terminal of the bank 401 from which battery has been removed and which corresponds to cord circuit C is found. lVhen the cord finder has arrived at this point, the stepping magnet will stop its operation and relay 404 will operate. This relay has a high resistance winding and will operate in series with the stepping magnet Without causing the stepping magnet to operate. Relay 404 in operating locks in series with a resistance 405 through its right hand armature and front contact and remains in this condition until it is released by the operation of relays 406 and 407 as will hcrein after be described. The operation of relay .404 closes an obvious circuit for the operation of relay 409 which in turn closes a circuit for the operation of relay 410. Relays 403, 409 and 410 of the position finder E are individual to the group of cord circuits to which cord C belongs. Relay 410 will receive battery I01 its circuit through a seriescircuit through the outer left hand arma-tures and contacis of relays corresponding to the relay 408 n: dividual to other groups of cord circuits. The individual relays for each group of cord circuitscorresponding to relays 409 and 410 are connected in a manner similar to relays 403, 409' and 410. One set of such relays is shown to the left of the group of relays involved in this connection. On the operation of relay 410, an obvious circuit will be closed for relay 403, which by operating its right hand armature opens the connection thereover for the stepping mag net 400. Thus no other cord in the group of which cord C is one can cause cord finder D to operate until the release of cord C in the Snnr larly the operation of relay 410 by attracting its armature removes ground normally connected in a chain circuit through the ar matures of other relays corresponding to re lay 410 in other groups so that none of these relays can be operated while relay 410 is actuated. Thus connections for other cord circuits in other groups are prevented from going through the position tinder until the functions of cord circuit C are completed.

On the operation of relay 403 a circuit is closed for relay 412 as follows: battery, winding of relay 412, outer right hand armature and front contact of relay 403, left hand armature and front contact of relay 404 to ground. The operation of relay 412 closes a circuit from battery through bank 413 to the cord circuit C to cause the operation of the repeater selector F. This circuit may be traced as follows: battery, left hand armature and back contact of relay 414, in ner right hand armature and front contact of relay 408, outer ri ht hand armature and front contactof relay 412, winding of relay 415, brush and a terminal of bank 413, winding, armature and back contact of stepping magnet 416 of repeater finder F, right hand armature and back contact of relay 340 to the brush of bank 418 of the repeater finder F, and if the brushes of the repeater finder F do not happen to rest on the terminals of an idle repeater, that is, one that has no ground connected to it through the brush of bank 418, the stepping magnet 416 will start to operate and advance the brushes of repeater finder F until an idle repeater is found. In other words if a busy repeater is encountered ground will be connected to brush 418 through the multiple contacts from the corresponding brush of the repeater finder connected with the busy repeater. This ground would be supplied from the right hand armature and front contact of the relays corresponding to relay 340 in the engaged cord circuits. Relay 415 in the above traced circuit is a fast operating relay as compared with relay 340 which is slow to operate. Thus relay 415 will operate and prevent relay 340 from operatin The circuit for relay 340 that will be completcd through the armature and back contact of relay 415 when relay 415 later releases may be traced as follows: battery, left hand armature and back contact of relay 414, inner right hand armature and front contact of relay 403, armature and back contact of relay 415, the brush and a terminal of bank 420, right hand winding of relay 340 to ground. The stepping magnet 416 will continue to operate until an idle repeater is found that is one which has no ground on its multiple terminals of banks such as 418. The circuit through the relay 415 and the stepping magnet 416 will therefore be opened and consequently cause the release of relay 415 and the stopping of magnet 416. lVhen this takes place, the previously traced circuit for relay 340 will be completed through the armature and back contact of relay 415 so that this relay 340 will now be energized and apply ground through its left hand armature and front contact to brush of bank 418 thus making the repeater G busy to other cords. Relay 340 in operating provides a locking circuit for itself through its left hand winding, armature and front contact to ground at the in ner upper armature and front contact of relay 330.

The operation of relay 840 closes a circuit for relay 422 as follows: battery, winding of relay 422, the selected terminal and the brush of bank 418, right hand armature and front contact of relay 340 to ground. The operation of relay 422 provides a ground for the operation of relay 414 over an obvious circuit. This latter relay in operating removes the multiple battery for the cord finder F through the position finder E. The operation of relay 122 also connects ground through the windings of relays 406 and 107 and its two outer right hand armatures and front contacts to terminals of the switches P and N of the links K and H respectively, to mark the terminals of repeater G in the levels in which all the terminals of repeater G terminate on. switches P and N. The operation of relay 422 also closes a circuit for the operation of relay 125 over a circuit as follows: battery, winding of relay 425, outer left hand armature and back contact of relay 406, inner right hand armature and front contact of relay 422 to ground. Relay 125 is common to all repeaters that have their terminals represented in one level on the switches P and N and the operation of this relay therefore marks this level on switches P and N by closing its armaturcs and front cont-acts to ground. As shown for switch N, the terminal 205 is marked with the ground from relay 425 and terminal 605 of switch P is marked with the ground from relay 425.

The operation of relay 3 10 also closes at its left hand armature and front contact a connection from ground at the relay 330 for the operation of relay 350. This circuit may be traced as follows: battery, winding of relay 350, left hand armature and front contact of relay 3 10 to the ground at the upper inner armature and front contact of relay 330. The purpose of the operation of relay 350 will become apparent as the description proceeds. It should be noted that relay 351 was operated at the time of the operation of relay 330 through a circuit as follows: battery, winding of relay 351, left hand armature and back contact of relay 352 to the ground at the upper inner armature and front contact of relay 330. As this relay is operated at the time of operation of relay 340, a circuit is now closed for the operation of relay 316 as follows: battery, winding of relay 316, armature and front miintact of relay 351, left hand arn'iature and front contact of relay 340 to the ground at the upper inner armature and front contact of relay 330.

The operation of relay 316 now disconnects the relays 31 1 and 338 from the. sleeves of plugs 300 and 303. These relays, however, are maintained operated by the closing of the make-before-break contacts of relay 316 to ground through resistances as follows: The circuit for relay 31 1: may be traced as follows: battery, winding of relay 314, up per inner normal contacts of key 301, left hand make-beforc-break contacts of relay 316, high resistance 354- to ground, while the circuit for relay 338 may be traced from battery, winding of relay 338, lower inner normal contacts of key 301, right hand makel')eforebreak contacts of relay 316 through the higl'i resistance 355 to ground. The

sleeve circuits for the cord are now connected as follows: The sleeve of plug 300 is connected through the inner left hand armature and front contact of relay 316 through a low resistance 357 to ground, while the sleeve circuit from plug 303 is connected through the inner right hand armature and front contact of relay 316 through a high resistance 358 to ground.

The functions of the circuits for lines A. and B from now on are practically identical and therefore only the operations for line A, except where they differ from the operations of line B, will be described. The

application of ground through the. low re-v.

sistance 357 to the sleeve of plu 300 causes the release of relay 118 which in releasing provides a ground for the operation of relay 116, that is, relay 116 is momentarily operated, as relay 120 is slow to release, on the release of relay 118. However, the momentary operation of relay 116 causes certain functions to take place which willbe described hereinafter. The operation of relay 116 opens the circuit for relay 118 and connects the winding of relay 126 to the sleeve circuit which on finding the ground supplied by the operation of relay 316 operates over a circuit as follows: battery, winding of relay 126, lefthand armature and back contact of this relay, left hand armature and front contact of relay 116 to the ground through the resistance 357 at the left hand armature, and front contact of relay 316. Relay 126, in operating provides a locking circuit for itself as follows: battery, winding of relay 126, make-'before-break cont-acts of this relay, left hand armature and front: con tact of relay 123, outer right hand armature and back contact of relay 111. It should be noted that relay 123 is slow to release so that it will not release on the release of relay 120, which is merely released for the short period while relay 116 is operated, thatis, when relay 116 is released, the circuit for relay 118 is restored and on the operation of this relay, relay 120 is reoperated so as to provide a locking circuit for relay 123. The operation of relay 126 now connects the sleeve circuit through the left hand armature and front contact of relay 116 to the left hand winding of relay 128 which operates before relay 116 releases. Relay 128 is marginal and operates on the ground supplied through low resistance 357 by relay 316 It should be noted that in the case of the operation of the corresponding relays of line B the relay 528 in the circuit for line B, that corresponds to relay 128, does not operate as the circuit for this relay from relay 316 extends through the high resistance 358. The opera tion of relay 128 and the non-operation of relay 528 mark the difference between the call originating line A and the line B through which the connection is being extended. In other words, these relays determine that the line A shall be connected to the incoming and of repeater G and that line it shall be connected to the outgoing end of repeater G. Relay 128 in operating provides a locking circuit for itself to ground at the left hand armature and back contact of relay 111.

As stated, the function of the circuits of lines A and B are practically identical except for this marking of the lines, and, as this applies also to the functioning of the links H and K, the operation of the link H to connect line A to the incoming end of repeater G will be described, while the description of the connection of the line B to the outgoing. end of repeater Gr through the link K will be substantially omitted. While the above mentioned operations of the circuit of the line A take place, the relay 352 in cord circuit C is operated over a circuit as follows: battery, winding of relay 352, outer right hand armature and front contact of relay 316 to ground. This relay is looked through its left hand armature and frontcontact to ground at the inner upper armature and front contact of relay 330. Relay 352 in operating causes the release of relay 351 which in turn releases relay 316 so that the sleeve circuits are now restored to normal condition to allow the reoperation of relay 118. The release of relay 116 as previously described now causes the operation of relay 131 over a circuit as follows: battery, winding of relay 131, left hand armature and front contact of relay 128. right hand armature and front contact of relay 126, right hand armature and back contact of relay 117 to ground. It should be noted that in the case of the circuit for line B due to the fact that relay 528 is not operated. relay 532 will operate instead of relay 531 corresponding to relay 131 in the circuit for line A. The operation of relay 131 in one case and relay 532 in the other case marks a distinction in the links H and K so that in the first case the link H will be used for e.\' tendinga connection to the incoming end of repeater G. whereas in the case of line B the link K will he used for connecting line B to the outgoing end of repeater G. The operation of relay 131 causes the following functions to be performed: A ground is provided for the operation of relay 136 over an ob vious circuit. A connection is provided for relay 137. for the marking of a terminal. 207 for line A on the switch M in the level of the switch in which the terminals for line A appear. The operation of relay 131 also connects at its right hand armature and front contact a control lead from line A to link H, the purpose of which will become apparent as the description proceeds. The rel y 136 s omm n t all he toll line have ing terminals appearing in the level in which the line A appears so that on the op,- cratlon of this relay, this level is marked by a ground from the outer right hand armature and front contact of relay 136 to the contact 237 of switch M, the level in this case being the third in the group.

The relays 210 and 211 in the link H pro Yide means for distributing the so-called starting ground from the toll lines to links such as H so that a toll line in this group now going through a connection is immediately connected to the first idle link. In this case it has been assumed that link H is idle so that relay 136 besides marking the level of this particular line also provides a ground for starting the operations of link H. This starting ground causes the operation of relays 213 and 21 1 over a circuit as follows:

-The circuit for relay 213 may be traced from battery, Winding of relay 213,-vertical off normal contacts for switch M, ina e-befor' break contacts of relay 210 to the ground at the inner right hand armature and front contact of relay 136, while the circuit for relay 21 i nay be traced from battery, winding of relay 21 1, vertical off-normal contacts for switch N through the make-beforehreak contacts of relay 210 to the above mentioned ground at the inner right hand armature and front contact of relay 136. The relays 213 and 214 provide locking circuits for themselves through their 11th rotary step contacts, left hand armatures and back contact of relay 216 to ground. The operation of relays 213 and 214 provide battery for the operation of relays 220 and 218. The circuit for relay 220 may be traced from battery, right hand armature and front contact of relay 213, armature and back contact of the vertical magnet 220, armature and back contact of the rotary magnet 221, winding of relay 220 to ground, while the circuit for relay 218 may be traced from battery, left hand armature and front contact of relay 214, armature and back'contact of vertical magnet 222, armature and back contact of rotary magnet 223, winding of relay 218 to groan d. The vertical magnet 217 will now start to advance the brushes of switch M in a vertical direction to the level in which the terminals of line A are located and simultaneously a vertical magnet 222 will start to move the brushes of switch N in a vertical direction to the level in which the terminals of the repeater G are located. The circuit for the vertical magnet 217 may be traced as follows: battery, right hand armature and front contact of relay 213, inner left hand armature and back contact of relay 225, winding of magnet 217 right hand armature and back contact of relay 226, armature and front contact of relay 220 to ground. While the operating circuit for t e vertical magnet 222 mayv be traced battery, left hand armature and front contact of relay 214, inner left hand armature and back contact of relay 211, winding of vertical magnet 222, outer left hand armature and back con tact of relay 229, armature and front contact of relay 218 to ground. T hose vertical magnets therefore continue to step until ground is found on the marked contacts of the levels in which the terminals of the line A and repeater G are located. VVht-n these levels are reached, relays 226 and 220 are operated removing ground from the vertical n'iagnets and transferring it to the rotary magnets. The circuit for relay 220 may be traced as follows: battery, rigl'it hand armature and front contact of relay 213, inner left hand armature and back contact of relay 225, right hand winding of relay 226, brush 230, the marked terminal 237 of switch M to ground at the outer right hand armature and front contact of relay 136, while the circuit for relay 229 may be traced as follows: battery, left hand armature and front contact of relay 21 1, left hand inner armature and back contact of relay 211, left hand winding of relay 229, brush 231, the marked terminal 205, left hand armature and front contact of relay 425 to ground. Relays 226 and 229 provide locking circuits for themselves through their secondary windings to ground under the control of relays 213 and 214, respectively. The rotary magnets 221 and 223 are now energized for the stepping of the brushes of switches M and N around the terminals, in the levels to which they were advanced, to the terminals of lines A and repeater G marked by the operation of relays 131 and 4-22, respectively. The circuit for rotary magnet 221 may be traced as follows: battery, right hand armature and front contact of relay 213, inner left hand armature and back contact of relay 225, winding of magnet 221, right hand armature and front contact ofrelay 226, armature and front contact of relay 217 to ground, while the circuit for rotary magnet 223 may be traced from battery, left hand armature and front contact of relay 21 i, inner left hand armature and back contact of relay 211, rotary magnet 223, left hand armature and front contact of re lay 229, armature and front contact of relay 218 to ground. When the brushes of switches M and N find the terminals marked, ground is connected to operate the relays 225 and 211. The circuit for relay 225 may be traced follows: battery, upper made contacts of the vertical off-normal contacts for switch M, right hand winding of relay 225, brush 232, terminal 207, left hand outer armature and front contact of relay 131, winding of relay 137 to ground. Relay 137 is marginal and does notoperate in this circuit. The circuit for relay 211 may be traced as follows: battery, made contacts of the vertical off-normal contacts for switch N, right hand winding of relay 211, brush 233, terminal 23 1-, outer right hand armature and front contact of relay 122, right hand winding of relay 07 to ground. Relay 4l07 is marginal and does not operate in this circuit.

From this point on the operations of switches hi and N will be described separately. ll hen relay 211 of switch N operates, it removes the battery from the ro tary magnet 223 by opening the connection between the inner left hand armature and its corresponding back contact and releases relay through the opening of the same contact. Relay 211 in operating prov1des a locking circuit for itself through its left hand winding and inner left hand armature and front contact to the battery on the left hand armature and front contact of relay 21 1. While the operations of the switches M and N begin simultaneously it is evident that the switches will not complete the1r operations at the same time as they may have to travel different distances to find their respectively marked terminals. Hence not until. both relays 211 and 225 are operated does a circuit for the operation of relay l0? become closed. This circuit may be traced as follows: battery, outer left hand armatin'e and front contact of relay 225, outer left hand armature and front Contact of relay 211, brush 233, terminal 234, outer left hand armature and front contact of relay 122, left hand winding of relay e07 to ground. clay -l07 now operates. It should be. noted that the non-inductive secondary winding of relay 4:07 normally shunts the active winding of relay, which is therefore not operated until this direct battery is connected to its circuit. The terminal 231- of the incon'iing end of repeater G is now made busy to other switches of links such as The operation. of relay 225 of switch M. removes the operating battery for the rotary magnet by separating its inner left hand armature from the corresponding back contact and this relay also causes the release of relay 220 through the same contact. Relay 225 in operating performs the following functions. it provii cs a locking circuit for itself through its left hand winding, inner left hand armature and front Contact to the battery a" the right hand armature and front contact of relay 213'. It supplies direct battery to the terminal 207 for the operation of relay 137 and for making this terminal busy. The circuit for relay 1.37 may be traced as follows: battery, right hand armature and front contact of relay 213,

second left hand armature and front contact of relay 225, brush 232, terminal 207, outer left hand armature and front contact of relay 131, winding of relay 137 to ground. The marginal characteristics of relay 137 are such that it does not operate on the operation of relay 225 through its winding but will operate now on the application of direct battery through the circuit traced. Relay 225 also provides battery through its outer left hand armature and front contact for the operation of. relay 407 as hereinbc fore described. Another circuit closed by the operation of relay 225 is one for the operation of relay 210. This circuit may be traced from battery through the right hand winding of relay 210, the third left hand armature and front contact of relay 225 to ground. This ground also completes a circuit for the operation of relay 238 from the battery at the inner left hand armature and front contact of relay 211. It should be noted that relay 238 does not operate until both switches M and N have found the desired terminals.

The operation of relay 210 transfers, by opening its make-before-break contacts and closing its left hand armature to its inner front contact, the starting ground lead from relay 136 to the next link. Of the next link only the relay 210 corresponding to relay 210 has been shown. The operation of re lay 137 causes the release of relay 136 as no other multiple ground can be connected to its winding until this connection is completed, that is, until the cord and position finders have been released. The operation of relay 137 provides a ground for the operation of relay 139 over a circuit as follows: battery, winding of relay 139, armature and back contact of relay 140, left hand armature and front contact of relay 137 to ground; Relay 139 in operating connects alternating current from the source 144 through the two upper armatures and front contacts and the two lower armatures and front contacts, to the four leads from the line A to the brushes of switches M and N through the armatures and front contacts of relay 138 to the repeater Gr. It should be remembered that the relay 238 was previously operated to close these leads through from brushes of switch M to the brushes of switch -N. Ringing current will therefore be applied through these transmission leads to the repeater G to burn out or clean the contacts of these two switches, that is, the ringing current will destroy the dust particles that may have gathered on the brushes of these switches and cause them to make beliter contact with their respective termina s.

As stated, the operations of the link K are practically identical to the operations of link H. In this case the selection of the link K, that is, the link K of a pair K and L having access to the outgoing terminals of repeaters is, as previously suggested, effected by the operation of relay 532. This relay causes the operation of relay 550 and, closes a cirof the repeater of link K has progressed to the point where the operation of relay 406 is effected in the same manner as the operatlon of relay 407 was effected, a connection to ground is provided through the inner right hand armature and front contact of relay 407 and inner left hand armature and front contact of relay 406 for the operation of relay 428. The operation of relay 428 closes an obvious circuit for the operation of relay 429 and this relay in operating closes an obvious circuit for the operation of relay 430. Relay 430 in operating provides a locking circuit for itself through its left hand armature and front contact to the ground at the inner right hand armature and front contact of relay 407. Relay 430 in operating opens the circuit for relay 428 which in releasing causes the release of relay 429.

As soon as the toll operator has finished his conversation with the operator at the opposite end of line B, relating to the extension of the connection, she will release the telephone key 301 and in so doing cause the release of relays 321 and 311. When relay 321 is released, a circuit will be completed for the operation of relay 431 as follows: battery, upper outer armature and back contact of relay 321, inner right hand armature and front contact of relay 352, bank 433 of repeater finder F, left hand armature and back contact of relay 429, right hand armature and front contact of relay 430, left hand winding of relay 431, to ground. The operation of relay 431 removes the usual short-circuits from the bridge points on the repeater G and prepares the repeater for transmission. The cycle of operation just described of relays 428, 429, 430 serves as a means for allowing time for the burning out of the finder contacts of the links H and K, as hereinbefore described, before the repeater G is actually included in the connection. It should be noted that a circuit is also closed from the battery at the upper outer armature and back contact of relay through the contacts of relays 429, 430, 422 and 414, for the operation of relay 140 of the circuit for line A and also the corresponding relay 540 of the circuit for line B. The operation of these relays removes the ringing current from the contacts of the links H and K by causing the release of relays 139 and 539. The release of these relays 139 and 539 closes through the circuit from the battery at the upper armature and back contact of relay 321 to the windings of relays 142 and 542. These relays in operating disconnect the talking conductors of the toll lines A and B respectively from the cord C and connect these lines and their respective networks N, and N, to the repeater through the connections set up by the links H and K. The connection from lines A and B through the repeater G is now completed for transmission purposes. It seems unnecessary to trace the circuit from one line to the other through the repeater as it is quite obvious from the drawing how this connection is made.

It might be explained here that if during the vertical movement of the finders in the links, the marking of the terminals should for any reason be passed over by the commutator brushes 230 and 231 of the finders M and N respectively and brushes 630 and 631 of finders O and P respectively, the vertical magnets will continue to step the brushes up until the 10th level is reached. Relay 229 or 629 would then operate from ground through brush 231 for example, at the 10th level contacts. In this case, the rotary magnets will operate to step the brushes over this'level until the 11th rotary step is made at which time the brushes would actuate the 11th step rotary contacts such as for example, 240 for switch M- and 241 for switch N. The operation of these contacts causes the release of relays 213 or 214 and provides battery for the operation of the release magnets such as 242 for switch M or 243 for switch N so that the finders will be restored to their normal positions. hen this takes place, the vertical off-normal contacts of the respective finders are restored to normal position allowing ground from the relay 136 to reoperate the relays 213 or 214 andthus again start the brushes hunting for the desired line or repeater connection. This sequence of operation will continue until the brushes find the marked terminals or the time alarm circuit T functions, in which case the whole connection is restored to normal and an alarm signal is operated by this circuit T as will hereinafter be described.

The time alarm circuit T operates as follows: On the operation of relay 412 a circuit is provided for the operation of stepping magnet 436 as follows: battery, outer right hand armature and back contact of relay 437, armature and back contact and winding of stepping magnet 436, outer left hand armature and back contact of relay 437 to ground at the outer left hand armature and front contact of relay 412. As the stepping magnet 436 operates, the brush of bank 438 moves one step and as this brush connects to ground on the next terminal the relay 437 is operated over a circuit as follows: battery, inner right hand armature and front contact of relay 412, winding of relay 437, make-before-break contacts of this relay, winding of magnet 436 to ground at the second terminal of bank 438. Relay 437 looks up to the ground at the outer left hand armature and front contact of relay 412. Relay 437 in operating provides battery for the operation of relay 440 through the interrupter 441. Relay 440 in operating closes a circuit for the operation of stepping magnet 436 as follows: battery, outer right hand armature and front contact of relay 437, armature and front contact of relay 440, winding of stepping magnet 436, brush of bank 438 to ground at the second tern'iinal. Interrupter 441 will now interrupt this connection to ground at certain intervals. This interrupter, therefore, alter nately operates and releases relay 440 so that the battery at its armature and front contact will be alternately connected and removed from the circuit for stepping magnet 436. The stepping magnet will therefore advance the brushes of banks 438 and 442 step-by-step under control of the interrupter 441. If this condition prevails for a cer-. tain period, for example for 5 seconds, the brushes will have been advanced to a predetermined position. An alarm will then be given and the position finder and cord finder will be released to prevent holding up of the system. If, for example, for any reason the system has failed to function within this period, the brush of the bank 442 will.

be advanced to a terminal 443. In this position ground from the inner right hand armature and front contact of relay 437 through brush 442 will be connected to terminal 443, through the inner left hand armature and front contact of relay 412, the brush of bank 455, through the winding of relay 345 to battery. Relay 345 operates and locks under control of a key 360 at the toll operators position and releases the cord finder and position finder by placing battery from its middle right hand armature and front contact on the brush of bank 401, to release relay 404 and thus cause the release of the relays 409, 410 and 403 in succession to release the position finder E. The operation of relay 345 also closes a circuit at its outer left hand armature and front contact from battery through lamp 361 to ground through the I winding of relay 362. Lamp 361 lights and indicates to the operator that the circuit has failed to function properly and the opera tion of relay 362 closes a circuit for relay 363 through an interrupter 364. The operation of relay 362 also closes a circuit for a lamp 365 and an alarm bell 373 which is common to the oflice in which the toll operator islocated. The relay 363 is alternately operated and released by the inter rupter 364 to flash the lamps 313 and 337 of cord C to indicate this cord as being the one involved in the unsuccessfulconnection. The operation of key 360 will restore the circuit to normal condition. 7

Assuming however, that the repeater is in serted in the connection within the allotted.

time, the time alarm circuit will not function to give an alarm due to the release of relay 412 as will hereinafter be described. Relay 412 in releasing causes the release of relay 437 which now causes the stepping magnet 436 to actuate the brushes of links 438 and 442 to advance to the next rest position 443 or 445 andthus prevent an alarm from being operated.

In case all of the repeaters are busy, battery through bank 413 of the cord finders, such as D, will not be available as all relays, such as 414, will be actuated. However, battery through the high resistance winding of relay 450 of the common meter circuit It will be available. The high resistance of the winding of relay 450 will prevent relays such as 340 from becoming operated but will allow the operation of relay 450 and relay v369. The circuit for these relays may be traced as follows: battery, winding of relay 450, inner right hand armature and front contact of a relay, such as 403, armature and back contact of a relay, such as 415, banks such as 420, winding of a relay, such as 340 to ground. The circuit for a relay, such as 369, will be as follows: battery, right hand winding of a relay, such as 369, a bank such as 454, inner right hand armature and front contact of a relay, such as 403, to ground through the right hand winding of relay 340. On the operation of relay 450 a circuit will be closed for the operation of the meter magnet 452 following the operation of the timing device T to indicate or count the number of times repeaters were required but were not available due to the fact that all repeaters were busy.

It should be understood that if a repeater becomes idle before the timing device operates the circuits will function to select this idle repeater in the manner hereinbefore described. Relay 369 in operating closes a locking circuit for itself through its right hand armature and front contact to the common ground at the inner upper armature and front contact of relays such as 330. The operation of this relay also closes a circuit from the interrupter 364 to the lamp 337 and this lamp is now flashed to indicate that no repeater is available. When a plug, such as 303, is removed the lamp 337 stops flashing as the above operations take place in the cord that has been taken for use for the establishing of a connection when it was found that a repeater was not available. g

If the operator has occasion to operate talking key 301, after a repeater has been connected to lines A and B, relay 321 will be operated and relay 431 and relays such as 142 and 542 will be released. The release of relay 431 short-circuits the bridge points of the repeater G and the release of the relays 142 and 542 disconnects lines A and B and their respective networks from the repeater G and connects the lines through the cord circuit and to the operators telephone. As the bridge relays, such as 105 and 505, are not disconnected from the cord circuit, incoming signals may be received over the toll lines.

hen plug 300 is removed from toll line A, relay 118 is released. This causes a mo mentary operation of relay 116, through a contact of relay 120, which is released soon after the release of relay 118. On the operation of relay 116 the remaining operated relays of the circuit for toll line A are restored to normal, such as, relays 131, 123, 126, 128 and 108. In the cord circuit C relay 314 is released and this relay in turn releases relay 330. The release of relay 330 connects battery from the armature and front contact of relay 350 to the ring conductor of the cord to cause the operation of relay 511. The operation of relay 511 removes ground from the locking windings of relays 508, 526 and 528, while relays 523, and 520 are held operated by relay 518. Relay 350 of the cord circuit releases, due to the release of relay 330 and consequently relay 511 will only be momentarily operated. The release of relay 330 by opening the common ground applied at its inner upper armature and front contact causes the release of relays 340, 352, 422, 406, 407 and 431. The release of relay 422 applies battery for the operation of the marginal relays 216, and 616 in the links H and K respectively. These relays are operated only on this battery from the outer right hand armature and back contact of relay 422. Relays 216 and 616 in operating open the holding circuits'for relays 214 and 614 and also for the relays 213 and 613 and the release of these relays causes the restoration of links H and K to normal as hereinbefore described.

While this invention has been described as particularly applicable to telephone toll con-* neat-ions, it may be incorporated in switching systems not operated on a toll basis.

What is claimed is:

1. In a telephone system, incoming lines, outgoing lilies, a common group of equipments, links having line finders and equipment finders, and means for actuating two of said links for Ending a particular one of said incoming lines, a particular one of said outgoing lines and an equipment and for interconnecting said equipment between said incoming and outgoing lines.

2. In a telephone system, lines, a group of selectable links, each link including means for modifying the transmission characteristics of lines connected with it, other links having line finders and link finders, and means for actuating two of said other links for finding two lines requiring said modi fying means and each end of a selectable link and for interconnecting said modifying link between said two lines. 

